The invention relates generally to micro-electromechanical systems (MEMS) for high voltage switching applications. More particularly, the invention relates to highly resistive gate electrodes for MEMS devices, and devices incorporating such gate electrodes. The invention also relates to method of making such MEMS devices.
Microelectromechanical systems (MEMS) devices are being developed for an enormous variety of industrial and medical applications because these device have several potential advantages, including low cost, high reliability, and performance advantages achieved through miniaturization. Potential applications include actuators, sensors, switches, accelerometers, modulators and other micro-devices. MEMS devices integrate electrical and mechanical components that are generally fabricated using integrated circuit processing technologies.
Emergence of MEMS technologies has brought global attention to the possibility of merging conventional macroscopic relay attributes with MEMS device attributes to produce MEMS based relays/switches. MEMS switches have advantages over their conventional counterparts. The potential for high power efficiency, low insertion loss, excellent isolation, and ability to integrate with other electronics makes microswitches an attractive alternative to traditional mechanical and solid state switches. Most MEMS based relays/switches have been developed for signal switching applications and a few for power applications.
One well-known type of MEMS switch operates through the electrostatic actuation of a beam or cantilever to achieve physical contact with an electrode. The beam is deflected electrostatically by an actuation or gate electrode. The electrostatic forces due to the electric field between the beam and the gate electrode can generate relatively large forces in the small separations. Thus, in the actuated state, there is a chance that the beam may touch the gate electrode and short the device. To avoid any contact, the gate electrode may use a dielectric layer deposited over the conductive material, thereby insulating the gate from the beam. The choice of dielectric is constrained by switching properties such as actuation voltage and the field across the dielectric. For example, the dielectric should have higher breakdown voltage than the field across the dielectric.
Conventionally, the dielectric layers are deposited over gate conductive material by using vapor deposition methods such as plasma enhanced chemical vapor deposition (PECVD). These layers are generally of low quality and may be easily attacked by the processing and operating environments.
While the dielectric layer serves the above purpose, the layer may also experience a dielectric charging phenomenon. Over time and cycles of actuation, a charge may accumulate within the layer and build up a field that screens the applied field. This alters the gate voltage required to actuate the switch, which may cause inaccuracy and failure of the switch.
Thus, there is a need to provide an improved dielectric material for MEMS devices. There is a further need for MEMS devices for high voltage switches with improved properties as compared to conventional switches. Moreover, there is a need for methods to produce such dielectric layers and MEMS devices.